Engineers have fitted the last major piece into what they claim is the world's largest scientific instrument – the nuclear particle accelerator filling a 27km (17-mile) circular tunnel under the Swiss-French border.
"It's exciting, but at the same time there is a feeling of relief," said Robert Aymar, the French director general of the European Organisation for Nuclear Research.
The start-up date for the Large Hadron Collider, which will be used by scientists to study the make-up of matter and the universe, has yet to be set. But Dr Aymar said the €1.3bn (£1bn) project, which has been under construction since 2003, was on target to begin work this summer.
The various chambers in the tunnel – built with the help of more than 20 countries – will join in recording what happens when protons collide at the speed of light. When it is finished, scientists will lower the temperature section by section to near absolute zero – colder than outer space. Thousands of scientists from 80 countries will then use it for experiments.